Using a non-reactive sauce pot- Melt butter, water, and salt and bring to a simmer and lower flame.

Mix the xanthan gum and flour together.

Using a wooden spoon, add flour mixture to water, all at once. Stir with a wooden spoon until a smooth dough forms.

Reduce heat to medium low and continue to stir, beating dough forcefully and rapidly to prevent it from sticking to the pot.

Continue cooking until the dough pulls away from the sides of the the pot.

Place this cooked mixture into a large stand up mixer and mix on low until mix is cool and is no longer steaming hot.

While still mixing on low add eggs one at a time, and allow them to fully incorporate before adding the next.

After all egg is incorporated mix in pecorino, parsley and mustard.

The dough should pull away from the side of the mixing bowl slightly, and should not be overly tacky, this is the indication that you have added enough eggs and you may or may not need the one you had reserved.

If using fresh peas, cook in a medium saucepan of boiling salted water until tender, about 3 minutes (if using frozen peas, do not cook). Drain, transfer to a bowl of ice water, and let sit until cold, about 3 minutes. Drain and pat dry.